The present invention relates to an electrophotographic photoconductor comprising an electroconductive support and a photoconductive layer comprising (i) a charge generation layer and (ii) a charge transport layer formed on the support, and more particularly to an electrophotographic photoconductor in which the charge generation layer comprises a charge generating material and one component selected from the group consisting of an aliphatic alcohol and a crown ether, or the charge transport layer comprises a charge transporting material and one component selected from the group consisting of an aliphatic alcohol, a polyalkylene glycol, a polyalkylene glycol ester, a polyalkylene glycol ether and a crown ether.
Conventionally, electrophotographic photoconductors comprising a charge generation layer which contains a variety of resins as well as charge generating materials are employed. As such resins, polyvinyl butyral (Japanese Laid-Open patent application No. 58-105154), cellulose esters of fatty acids (Japanese Laid-Open patent application No. 58-166353), an acrylic resin having a glass transition temperature (Tg) of 70.degree. C. or less, and an oxidation number of 10 to 40 (Japanese Laid-Open patent application No. 58-192040), a mixture of a resin having a glass transition temperature (Tg) of 70.degree. C. or less and a resin having a glass transition temperature (Tg) of 75.degree. C. or more (Japanese Laid-Open patent application No. 58-193549), a composition of a charge generating material, a resin and a solvent, to which another composition of a resin having a small compatibility to the first mentioned resin, and a solvent, is added and redispersed (Japanese Laid-Open patent application No. 56-12646), polyvinyl pyrrolidone (Japanese Laid-Open patent application No. 56-113140), and polyvinyl formal resin (Japanese Laid-Open patent application No. 61-235844) are employed.
However such conventional photoconductors have the shortcoming that the photosensitivity and the chargeability related to the pre-exposure fatigue of the photoconductors vary, depending upon the mixing ratio of a charge generating material and a resin binder.
In other words, when the weight ratio of a resin binder to a charge generating material is decreased, a higher photosensitivity can be obtained, but the chargeability is considerably decreased due to the pre-exposure fatigue. In contrast to this, when the weight ratio of a resin binder to a charge generating material is increased, the tendency for loss of the chargeability can be suppressed, but the problem occurs that the photosensitivity is significantly reduced.
The conventional photoconductors have another shortcoming that the surface potential considerably deteriorates during the repetition of the cycle of charging and exposure.
Furthermore a variety of organic electrophotographic photoconductors are proposed, for instance, a photoconductive resin type photoconductor typified by polyvinyl carbazole (PVK), a charge transport complex type typified by PVK-TNF (2,4,7-trinitro-fluorenone), a pigment dispersion type typified by a phthalocyanine-binder, and a function-separated type in which a charge generating material and a charge transporting material are combined. Among them, the last type especially attracts attention.
When a high-photosensitive photoconductor of such a function-separated type is applied to the Carlson process, it has the shortcoming that it exhibits a low chargeability and a poor electric charge retention (sharp dark decay). Furthermore, the chargeability and electric charge retention properties are drastically degraded in the course of repeated and continuous use, which cause uneven image density and fogging. Furthermore, the deposition of toner particles on the background occurs when reverse development is performed.
In general, the high-photosensitive photoconductors show the reduction in the chargeability due to the pre-exposure fatigue. Such fatigue is mainly caused by the light-absorbed charge generating materials. Therefore it is considered that the longer the period in which the electric charges generated by light absorption remain in a movable state in the photoconductor and the greater the number of the generated electric charges, the greater the reduction in the chargeability caused by the pre-exposure fatigue of the photoconductor. Even if the photoconductor is electrically charged in a state where the electric charges generated by light-absorption remain therein, the surface potential is not elevated until the residual electric charge is dissipated. This is because the electric charges at the surface of the photoconductor are neutralized by the transport of the residual carriers in the photoconductor. Thus, the rise of surface potential is delayed in such a manner as to correspond to the pre-exposure fatigue, and accordingly the apparent surface potential is lowered.
In order to solve the above-mentioned shortcomings, intermediate layers made of cellulose nitrate resins are disclosed in Japanese Laid-Open patent application Nos. 47-6341, 48-3544 and 48-12034; intermediate layers made of nylon resins in Japanese Laid-Open patent application Nos. 48-47344, 52-25638, 58-30757, 58-63945, 58-95351, 58-98739 and 60-66258; intermediate layers made of maleic acid resins in Japanese Laid-Open patent application Nos. 49-69332 and 52-10138; and an intermediate layer of polyvinyl alcohol resin in Japanese Laid-Open patent application No. 58-105155. Also, in order to control the electric resistivity of intermediate layer, intermediate layers which contain various electroconductive additives are proposed, for instance, an intermediate layer made of setting-resins to which carbon or a chalcogen material is added as disclosed in Japanese Laid-Open patent application No. 51-65942, an intermediate layer made of a polymer thermally polymerized by use of an isocyanate setting-agent to which a quaternary ammonium salt is added as disclosed in Japanese Laid-Open patent application No. 52-82238, an intermediate layer made of a resin to which a resistivity controlling agent is added as disclosed in Japanese Laid-Open patent application No. 55-1180451, an intermediate layer made of a resin to which aluminum oxide or tin oxide i dispersed as disclosed in Japanese Laid-Open patent application No. 58-58556, an intermediate layer made of a resin in which an organometallic compound is added as disclosed in Japanese Laid-Open patent application No. 58-93062, intermediate layers made of a resin in which electroconductive particles are dispersed as disclosed in Japanese Laid-Open patent application Nos. 58-93063, 60-97363 and 60-111255, and intermediate layers made of resins in which finely-divided particles of TiO.sub.2 and SnO.sub.2 are dispersed as disclosed in Japanese Laid-Open patent application Nos. 59-84257, 59-93453 and 60-32054.
From the viewpoint of controlling the electric charge transport instead of the electric resistivity, intermediate layers made of resins which contain an electron-acceptor organic compound serving as a negative charge transport material are disclosed. Examples of such intermediate layers are a photoconductive intermediate layer made of an organic polymer to which polycyclic aromatic nitro compound is added as disclosed in Japanese Laid-Open patent application No. 53-89433, and intermediate layers made of resins which contain an electron-acceptor organic material as disclosed in Japanese Laid-Open patent application Nos. 54-4134, 59-160147 and 59-170846.
In spite of employment of the above-mentioned intermediate layers, the reduction in the chargeability caused by the repeated and continuous use of the photoconductors, in particular, the delay in the rise of the surface potential thereof, is not sufficiently improved.